This application relates generally to seismic prospecting, and in particular to sensor arrangements for gathering seismic data. Suitable applications include, but are not limited to, seismic nodes for use in marine seismic surveys.
In towed marine seismic exploration, a hydrophone array is typically towed behind a marine vessel near the sea surface. The hydrophones are mounted to multiple sensor cables, commonly referred to as streamers. The streamers serve as platforms or carriers for the hydrophones, which are distributed along the length of each streamer in the array.
A set of seismic sources, also towed near the sea surface, are operated to periodically emit acoustic energy. The acoustic energy of interest propagates downward through the seawater (or other water column), penetrates the ocean floor, reflects from the subsea strata and other underlying structures, and returns upward through the water column to the hydrophone array.
The reflected seismic energy (or acoustic wave energy) arrives at receiver points in the towed hydrophone array. The array includes many such receiver points, distributed along each of the streamer cables, with sensors configured to generate data records characterizing the upward-traveling acoustic wavelets (or seismic waves) received from the subsurface structures beneath the seabed, at each of the receiver points. The hydrophone data recordings are later processed to generate seismic images of the underlying structures.
Noise is a major consideration in towed streamer operations. Noise sources encompass both coherent and random (or incoherent) effects, including, but not limited to, marine life, source bubble events, vessel noise, swell noise, and wave noise arising from the sea surface. Towing the streamers also generates noise due to flow effects as the streamers travel through the water column, and due to the seismic system sensitivity to acceleration.
Some of these noise components propagate through the streamers (or streamer cables), and some propagates through the water column itself. The presence of such noise contributions can adversely affect the accuracy of the sub-surface images, which are obtained from the processed seismic data. As a result, there is an ongoing need for more advanced marine seismic survey techniques, with reduced noise and improved seismic image quality.